A solid polymer type fuel cell uses solid polymer such as ion-exchange resin as an electrolyte, and is characterized by relatively low operating temperature. The solid polymer type fuel cell has, as shown in FIG. 1, a basic structure wherein a space surrounded by cell bulkhead 1 having a fuel flow hole 2 and oxidizing agent gas flow hole 3, respectively communicated with outside, is divided by a membrane assembly in which an anode 4 and a cathode 5 are joined to respective surfaces of a solid polymer electrolyte membrane 6, to form an anode chamber 7 communicated with outside via the fuel flow hole 2 and a cathode chamber 8 communicated with outside via the oxidizing agent gas flow hole 3. Then, in the solid polymer type fuel cell having the above basic structure, a fuel including hydrogen gas or liquid fuel such as methanol, etc. is supplied into the anode chamber 7 via the fuel flow hole 2, and oxygen or oxygen containing gas such as air to act as an oxidizing agent is supplied into the cathode chamber 8 via the oxidizing agent gas flow hole 3. Furthermore, an external load circuit is connected between both gas diffusion electrodes to generate electric energy by the following mechanism.
When using a cation-exchange membrane as the solid polymer electrolyte membrane 6, a proton (hydrogen ion) generated by contacting a fuel with a catalyst included in the electrode in the anode 4 conducts in the solid polymer electrolyte membrane 6 and moves into the cathode chamber 8 to generate water by reacting with oxygen in the oxidizing agent gas in the cathode 5. On the other hand, an electron, generated in the anode 4 simultaneously with the proton, moves to the cathode 5 through the external load circuit, so that it is possible to use the energy from the above reaction as an electric energy.
In a solid polymer type fuel cell wherein a cation-exchange membrane is used for such a solid electrolyte membrane, only an expensive noble metal catalyst is usable as a catalyst in the electrode because of its strongly acidic reaction field
Then, it has been examined to use an anion-exchange membrane instead of the cation-exchange membrane, and several of such solid polymer type fuel cells have been already proposed (Patent Articles 1 to 6). In a fuel cell using an anion-exchange membrane, catalysts other than noble metals can be used because the reaction field is basic. However, in this case, a mechanism for generating electric energy in a solid polymer type fuel cell is different in ion species moving through a solid polymer electrolyte membrane 6 as below. Namely, hydrogen or methanol, etc. is supplied to the anode chamber, and oxygen and water are supplied to the cathode chamber, by which the catalyst in the electrode is contacted with the oxygen and water at the cathode 5 to generate hydroxy-ion. This hydroxy-ion conducts in the above anion-exchange membrane as the solid polymer electrolyte membrane 6 and moves into the anode chamber 7 to generate water by reacting with fuel at the anode 4. An electron generated at the anode 4 is moved to the cathode 5 through an external load circuit, and the resulting reaction energy will be used as an electric energy.
In the solid polymer electrolyte type fuel cell using an anion-exchange membrane, it is further expected to greatly reduce crossover that the fuel such as methanol is permeated from the anode chamber side to the cathode chamber side. Furthermore, it is expected that, for example, overvoltage due to oxygen reduction can be reduced; that fuel containing carbon-carbon bond can be used; and that voltage can be improved due to selecting an inactive cathode catalyst to the crossover fuel, because of difference in atmospheres in both electrodes and because of expansion of the scope of available catalyst selection.
So far, it has been proposed for an anion-exchange membrane-type fuel cell to use a membrane obtained by filling up a porous membrane such as woven fabric with hydrocarbon-based cross-linked polymer having an anion exchange group such as quaternary ammonium base and quaternary pyridinium base (Patent Article 1), a membrane obtained by introducing a quaternary ammonium base into hydrocarbon-based engineering plastics followed by casting for film-forming (Patent Article 2), etc., as well as a membrane obtained by graft polymerization of a polymer containing fluorine as a base material with a hydrocarbon-based monomer having an anion-exchange group (Patent Article 3). Also, it is proposed to use a hydrocarbon-based elastomer hardly soluble in water and methanol (Patent Article 4) and resin quaternarized by a quaternarizing agent having a hydroxyl group (Patent Article 5) as an ionomer of a catalyst electrode layer, etc., as well as separation membrane with improved joining property with the catalyst electrode layer by adsorbing resin having a cation-exchange group onto the surface of the anion-exchange membrane (Patent Article 6).